Photoactive adhesion promoter

ABSTRACT

An adhesion promoter to help reduce semiconductor process effects, such as undesired line edge roughness, insufficient lithographical resolution, and limited depth of focus problems associated with the removal of a photoresist layer. A photoactive adhesion promoter (PAG) is described which helps reduce these and other undesired effects associated with the removal of photoresist in a semiconductor manufacturing process.

FIELD

[0001] Embodiments of the invention relate to the field of semiconductormanufacturing. More particularly, embodiments of the invention relate toa photoactive adhesion promoter to facilitate solubility of photoresiston a semiconductor wafer.

BACKGROUND

[0002] As feature sizes continue to decline in modernphotolithographical semiconductor manufacturing processes, effects, suchas undesired line edge roughness, insufficient lithographicalresolution, and limited depth of focus problems can increase. Moreparticularly, photoresist image footprints may become increasinglydifficult to control as semiconductor device features become smaller andcloser together.

[0003] Adhesion promoters may be used to bond the photoresist to thesemiconductor substrate or other device surface until the photoresist isexposed to light, thereby defining feature edges and boundaries withinthe device. Photoresist, however, may persist around the substratesurface and photoresist interface. This is because some regions towardthe bottom of the photoresist may not become sufficiently soluble afterbeing exposed to an incident radiation to be completely removed, andinstead remain bonded to the substrate by the adhesion promoter. Theseareas of persisting photoresist may correspond to areas where anincident radiation signal is weakest due to radiation absorption byphotoresist or reflective interaction effects between the substrate andphotoresist.

[0004]FIG. 1 illustrates a prior art adhesion promoter. The adhesionpromoter of FIG. 1 is a Hexamethydisilyazide (HMDS) adhesion promoterand serves to help bond the photoresist layer to the underlyingsubstrate. Accordingly, the adhesion promoter is removed along with thephotoresist after being exposed to incident radiation.

[0005]FIG. 2 illustrates a prior art process for forming an adhesionpromoter and photoresist layer on a semiconductor substrate. The priorart adhesion promoter of FIG. 1 is applied to a semiconductor substrate,followed by a photoresist layer being applied superjacent to theadhesion promoter. A mask layer is applied, exposing the photoresistlayer to incident ultra-violet light in areas that are not covered bythe mask layer. These process steps may also be applied to other layersof a semiconductor die.

[0006] The result of the above-described process step can be illustratedby the example of FIG. 3. FIG. 3 is a photograph of a line-spacingpattern illustrating roughness and poorly defined edges associated witha typical photoresist removal process. Particularly, FIG. 3 illustratesphotoresist deposits persisting between device features after beingexposed to an incident radiation, such as ultra-violet light.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments and the invention are illustrated by way of exampleand not limitation in the figures of the accompanying drawings, in whichlike references indicate similar elements and in which:

[0008]FIG. 1 illustrates a prior art adhesion promoter.

[0009]FIG. 2 illustrates prior art process steps for forming an adhesionpromoter and photoresist layer on a semiconductor substrate.

[0010]FIG. 3 is a photograph of a line-spacing pattern illustratingroughness and poorly defined edges associated with a typical photoresistremoval process.

[0011]FIG. 4 illustrates a photoactive adhesion promoter according toone embodiment of the invention.

[0012]FIG. 5 illustrates the steps for creating a photoactive adhesionpromoter according to one embodiment of the invention.

[0013]FIG. 6 illustrates process steps for forming and a photoactiveadhesion promoter and photoresist layer on a semiconductor substrateaccording to one embodiment of the invention.

DETAILED DESCRIPTION

[0014] Embodiments of the invention described herein help reducesemiconductor process effects, such as undesired line edge roughness,insufficient lithographical resolution, and limited depth of focusproblems associated with the removal of a photoresist layer. Moreparticularly, embodiments of the invention use a photoactive adhesionpromoter (“PAG”) to help reduce these and other undesired effectsassociated with the removal of photoresist in a semiconductormanufacturing process.

[0015] For at least one embodiment of the invention, these undesiredeffects are reduced by improving lithographical image fidelity at theregion around the interface of the adhesion promoter and the photoresistlayer. The optical signal incident to the exposed photoresist (thoseregions not covered by the mask layer) is effectively amplified at theadhesion promoter-photoresist interface region by allowing radiationincident to the exposed photoresist layer to be used more efficiently,thereby increasing the solubility of the photoresist in the interfaceregion.

[0016] Embodiments of the invention increase solubility of thephotoresist layer in the adhesion promoter-photoresist interface regionby using a photoactive adhesion promoter that releases a substance toenhance solubility of the photoresist in the interface region whenexposed to an incident radiation, such as ultra violet light.

[0017] For one embodiment, the substance is an acid that contacts thephotoresist, thereby increasing the photoresist's solubility so that itcan be removed more effectively. For other embodiments, the substance isa base, which would have the opposite effect upon the interface regionfrom an acid. The choice of whether to use an acid or a base isdependent upon the particular patterning and/or resist requirements ofthe application. Furthermore, a combination of acid and base may be usedin a photoactive adhesion promoter to further facilitate control offeature profile in the exposed adhesion promoter-photoresist interfaceregion. Other types of photoactive adhesion promoters may be blendedwith others for even greater diversity in feature control.

[0018]FIG. 4 illustrates a photoactive adhesion promoter (“PAG”)according to one embodiment of the invention. The example of FIG. 4illustrates a system that is capable of attaching a PAG to asemiconductor wafer as a self-assembled layer. The layer is bound to thewafer through the reaction of the trialkoxysilane with pendant groups,such as Si—OH groups and Si—NH₂ groups, on the wafer surface, therebyforming silylether linkages. These linkages are covalent bonds thatattach a photon harvesting group and a catalyst to the wafer surface.

[0019] The PAG of FIG. 4 comprises an adhesion promoter 401 and aphotoacid generator 405. The photoacid generator comprises a photonharvesting group 410 and a catalyst group 415. In the embodimentillustrated in FIG. 4, the adhesion promoter is trimethoxysilane, thephoton harvesting group is methyldiphenylsulfonium, and the catalystgroup is nonafluorobutanesulfonate. In addition, a linker 420 bonds theadhesion promoter to the photon harvesting group.

[0020] The adhesion promoter, photon harvesting group, and the catalystgroup may comprise different compounds as well. For example, theadhesion promoter may comprise alkoxysilane, silylchloride (a subclassof silylhalide), phosphate, phosphonate, alkene, thiol, or sulfide.

[0021] The photon harvesting group may comprise sulfonium salts, such astriarylsulphonium. Triarylsulphonium is a general class, in which arylrepresents any structure with an aromatic group bound to the sulfur atomas well as functionalized aryl groups where functionalization may beheteroatoms, such as fluorine, chlorine, bromine, and functional groupssuch as alcohol (OH), nitro (NO₂), amine (R₃N), amide (R₂NC(O)R),carboxylic acid (RCOOH), ester(RCOOR), ether (ROR), carbonate(ROC(O)OR).

[0022] Furthermore, alkyldiarylsulfonium and dialkylarylsulfonium are ageneral class of sulfonium salts which may be used, in which aryl isdefined as above and alkyl is a hydrocarbon group, such as (CH₂)_(n)CH₃where n=0 to 11, as well as functionalized hydrocarbon groups, in whichfunctionalization may be heteroatoms, such as fluorine, oxygen,nitrogen, chlorine, bromine and functional groups such as alcohol (OH),nitro (NO₂), amine (R₃N), amide (R₂NC(O)R), carboxylic acid (RCOOH),ester(RCOOR), ether (ROR), or carbonate (ROC(O)OR). Alternatively, thephoton harvesting group may comprise iodonium salts, such as diaryl andalkyaryl, in which aryl and alkyl are as defined above.

[0023] The catalyst group may comprise alternative compounds, such asperfluoroalkylsufonate, alkylsulfonate, arylsulfonate, alkyl and arylphosphate, or fluoroalkylamide.

[0024] For the embodiment illustrated in FIG. 4, the linker ismethylene. However, other compounds may be used, such as alkyl, whichmay include ethers, esters, carbonates, amides, amines as elements ofchains or side groups, wherein the side groups may also includinghalogen, alcohol, and nitrile. Alternatively, aryl may be used for thelinker, which may include functionalized aryl groups, which may beheteroatoms such as fluorine, chlorine, bromine, as well as functionalgroups such as alcohol (OH), nitro (NO₂), amine (R₃N), amide (R₂NC(O)R),carboxylic acid (RCOOH), ester(RCOOR), ether (ROR), or carbonate(ROC(O)OR).

[0025] By incorporating a PAG into an adhesion promoter, the adhesionpromoter-photoresist interface region becomes doped with acid whenexposed to light. This effectively amplifies the acid-catalyzed reactionwithin the photoresist. For the embodiment illustrated in FIG. 4, theeffect is catalytic, whereas in other embodiments the effect may beaccomplished using other methods. The acid generated by the PAG alsodisrupts adhesion in areas of positive tone resist where the photoresistis to be dissolved away after exposure to light. Advantageously, thephotoacid generator in the adhesion promoter confers an anti-reflectivequality to the surface upon which it is applied, thereby mutingradiation swing effects at the edges of the exposed region. Bymodulating surface energy differences between the photoresist and thesubstrate, the photoresist solubility at the resist-substrate interfaceand the optical properties of the interface are enhanced.

[0026]FIG. 7 illustrates a chemical structure of two other linkers thatmay be used in conjunction with at least one embodiment of theinvention. Specifically, FIG. 7 illustrates a flexible linker 701 and arigid linker 705. The choice of which linker to use depends upon theneeds of the device in which its used. FIG. 5 illustrates a method forcreating a photoactive adhesion promoter according to one embodiment ofthe invention. For the embodiment of the invention illustrated in FIG.5, an alkylsiloxane 501 is formed from combiningbromomagnesiummethylphenylphenylsulfide 505 and trimethoxysillychloride510 and treating the alkylsiloxane with methyliodide 515 to form asulfonium siloxane species 520. Furthermore, an ion exchange occurs as aresult of a silver salt of a nonafluorosulfonic acid being formed by theabove combination. Once the adhesion promoter is formed it can bepurified by recrystalization.

[0027]FIG. 6 illustrates a process for forming a photoactive adhesionpromoter and a photoresist layer on a semiconductor substrate accordingto one embodiment of the invention. A photoactive adhesion promoter isapplied to a semiconductor wafer in operation 601. A photoresist layeris applied superjacent to the photoactive adhesion promoter in operation605. A mask layer is overlaid on the photoresist layer in operation 610and an incident radiation, such as ultra-violet light, is introduced tothe exposed photoresist in operation 615. The resulting solublephotoresist is then removed in operation 620 to create a feature profilein the semiconductor device.

[0028] Various materials may be used in the embodiments of theinvention. For various embodiments of the invention, the substratesurface may be doped silicon, silicon dioxide, or other substratematerials.

[0029] While the invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments, which are apparent to personsskilled in the art to which the invention pertains are deemed to liewithin the spirit and scope of the invention.

What is claimed is:
 1. An adhesion promoter comprising: a photoacidgenerator to generate an acid upon exposure to incident radiation, thephotoacid generator comprising a photon harvesting group and a catalystgroup; and a linker to form a bond between the photoacid generator andthe adhesion promoter.
 2. The adhesion promoter of claim 1 wherein thephoton harvesting group is selected from a group consisting of sulfoniumsalts and iodonium salts.
 3. The adhesion promoter of claim 2 whereinthe catalyst group is selected from a group consisting ofnonafluorobutanesulfonate, perfluoroalkylsufonate, alkylsulfonate,arylsulfonate, alkyl phophate, aryl phosphate, and fluoroalkylamide. 4.The adhesion promoter of claim 3 wherein the linker is selected from agroup consisting of alkyl and aryl.
 5. The adhesion promoter of claim 1wherein the photoacid generator is to promote an anti-reflective qualityto a substrate surface upon which photoresist is applied.
 6. Theadhesion promoter of claim 5 wherein the photoacid generator is tomodulate surface energy differences between the photoresist and thesubstrate surface.
 7. The adhesion promoter of claim 6 wherein the acidis to promote solubility of the photoresist at an interface region ofthe adhesion promoter and the photoresist.
 8. The adhesion promoter ofclaim 7 wherein the photoacid generator is to covalently bond to thesubstrate surface as a self-assembled layer.
 9. A method of creating anadhesion promoter comprising: forming alkylsiloxane frombromomagnesiummethylphenylphenylsulfide and trimethoxysillylcholride;and treating the alkylsiloxane with methyliodide to form a sulfoniumsiloxane species.
 10. The method of claim 9 wherein an ion exchangeoccurs as a result of a silver salt of a nonafluorosulfonic acid beingformed.
 11. The method of claim 10 further comprising purifying theadhesion promoter, the purifying comprising recrystalization of theadhesion promoter.
 12. A process comprising: applying an adhesionpromoter to a semiconductor wafer, the adhesion promoter comprising aphotoacid generator to generate an acid in response to being exposed toan incident radiation to enhance solubility of a photoresist layerapplied superjacent to the adhesion promoter; and applying a photoresistlayer superjacent to the adhesion promoter; removing the photoresistlayer.
 13. The process of claim 12 wherein solubility of the photoresistlayer is enhanced by the adhesion promoter in an interface region of theadhesion promoter and the photoresist layer.
 14. The process of claim 12wherein the adhesion promoter reduces swing effects of radiationincident to the photoresist layer.
 15. The process of claim 12 whereinapplying the adhesion promoter comprises depositing trimethoxysilanesuperjacent a semiconductor substrate.
 16. The process of claim 15wherein the adhesion promoter is applied to the wafer in a solution ofethyl lactate.
 17. The process of claim 16 further comprising baking thewafer to bond the adhesion promoter to the wafer.
 18. The process ofclaim 17 wherein the adhesion promoter bonds to the photoresist via achemical catalyst group comprising nonafluorobutanesulfonate.
 19. Theprocess of claim 18 wherein the adhesion promoter comprises a photonharvesting group to enhance solubility of the photoresist, the photonharvesting group comprising methyidiphenylsulfonium.
 20. An apparatuscomprising: means for enhancing solubility of a photoresist layer, saidmeans for enhancing solubility being coupled to a photoactive adhesionpromoter; and means for forming a bond between the means for enhancingsolubility and the photoactive adhesion promoter.
 21. The apparatus ofclaim 20 wherein the photoactive adhesion promoter comprises a photoacidgenerator to generate an acid in response to being exposed to anincident radiation.
 22. The apparatus of claim 21 wherein thephotoactive adhesion promoter comprises a photobase generator togenerate a base in response to being exposed to an incident radiation.23. The apparatus of claim 22 wherein the photoactive adhesion promoteris to provide feature profile control of a semiconductor device.
 24. Theapparatus of claim 23 wherein the photoactive adhesion promotercomprises a photon harvesting group to receive the incident radiationand a chemical catalyst group to facilitate coupling between thephotoactive adhesion promoter and a photoresist layer.
 25. A methodcomprising: forming a photoactive adhesion promoter comprisingtrimethoxysilane, methyidiphenylsulfonium, andnonafluorobutanesulfonate, the photoactive adhesion promoter beingformed to enhance solubility of a photoresist layer applied superjacentto the photoactive adhesion promoter; applying the photoactive adhesionpromoter to a semiconductor substrate; depositing a photoresist layersuperjacent the photoactive adhesion promoter; exposing the photoresistlayer to light, the exposing causing a photoactive substance to begenerated to enhance solubility of the photoresist layer; and performinga process to remove the photoresist layer and the photoactive adhesionpromoter.
 26. The method of claim 25 wherein the photoactive substanceis an acid.
 27. The method of claim 26 wherein the photoactive substanceis a base.